This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-029351, filed on Feb. 6, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an authentication circuit, a semiconductor device having the authentication circuit, a process for operating the semiconductor device, an IC card having the authentication circuit, and a process for operating the IC card.
2. Description of the Related Art
Semiconductor devices, particularly, semiconductor memories having various properties are known. Among the semiconductor memories, particularly, those which retain data even when a power source is turned off are called nonvolatile memories. Among the nonvolatile memories, a nonvolatile memory which uses a ferroelectric as a material of a capacitor for holding charges and can be accessed at random is called a ferroelectric random access memory (FeRAM).
In the case where the material of a capacitor is not the ferroelectric, that is, a paraelectric, polarization is maintained only when there is a potential difference from an electrode. When the potential difference is eliminated, the polarization is not maintained, so that non-volatility is not exhibited and the memory becomes volatile. On the other hand, in the case where the material of the capacitor is the ferroelectric (in the case of the FeRAM), two residual dielectric polarization properties of different polarities are used and, even when the power source is turned off, polarization is maintained, data is retained and demonstrates non-volatility. In the case of the FeRAM, polarization can be achieved in one of two directions. By distinguishing the polarization direction, information xe2x80x9c1xe2x80x9d corresponding to polarization in one direction and information xe2x80x9c0xe2x80x9d corresponding to polarization in the other direction can be stored. The number of rewriting times as a measure of the performance of volatility is as many as 1010 to 1012. The rewriting speed is on the order of tens ns, so that high-speed performance is obtained. Consequently, recently, a system LSI using the ferroelectric is actively being developed.
Since the system LSI is used for a device using money information, personal information, and the like such as an IC card or Smart card, a countermeasure against forgery is indispensable in the system LSI. As a countermeasure against forgery, conventionally, for example, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 11-240227, a method for writing data into a storage area before scribing and then cutting out a pad being scribed in a data so that the storage area remains unaccessed is proposed. This method has, however, a problem such that since information has to be written into the storage area at the time of manufacturing a chip or mounting the chip onto a card, the method cannot be applied after a card is manufactured.
An object of the present invention is to provide an authentication circuit from which stored information cannot be decoded without being destructed, to/from which information can be written/erased even after the circuit is manufactured, and which is suitable for various devices from the viewpoint of forgery prevention, a semiconductor device having an excellent forgery preventing function suitable for a system LSI or the like, a process for operating the semiconductor device capable of performing a predetermined function while preventing forgery, an IC card having the excellent forgery preventing function, which is suitable for a Smart card or the like, and a process for operating the IC card, which can perform a predetermined function while preventing forgery.
A first authentication circuit of the present invention comprises at least two types of ferroelectrics comprising a ferroelectric 1 and a ferroelectric 2 having different Curie temperatures. Since the ferroelectrics have properties of retaining charges by residual polarization the ferroelectric functions as a nonvolatile memory. In the ferroelectrics, authentication signals as secret information for making a semiconductor device or the like perform a predetermined function are stored. When the authentication circuit is held at the Curie temperature of ferroelectrics 1 or higher and lower than the Curie temperature of the ferroelectric 2, an authentication signal stored in the ferroelectrics 1 is erased. When the authentication circuit is held at the Curie temperature of the ferroelectric 2 or higher, the authentication signal stored in the ferroelectric 2 is erased. Consequently, the authentication circuit is held at room temperature and operated, the authentication signal is output from the ferroelectric 1 to the ferroelectric 2, after that, the information stored in the ferroelectric 1 is erased. Subsequently, the authentication signal is output from the ferroelectric 2 to the semiconductor device or the like to make the semiconductor device or the like to perform a predetermined function. After that, the information stored in the ferroelectric 2 is erased. After conducting these operations, a third person cannot nondestructively re-transmit an output signal of the semiconductor device or the like stored in the authentication circuit. That is, if the third person could not give a predetermined temperature pattern corresponding to the Curie temperatures of the two or more types (n types) of ferroelectrics provided in the authentication circuit to the authentication circuit, a normal authentication signal stored in the authentication circuit cannot be output to the semiconductor device or the like. To output the normal authentication signal to the semiconductor device or the like, the third person has to destroy the authentication circuit to know the Curie temperatures of the two or more types (n types) of ferroelectrics provided in the circuit. Consequently, in the authentication circuit, authentication signals exists in the number equal to the number of the ferroelectrics provided in the circuit, and normal authentication signals are sequentially output only when a predetermined temperature pattern corresponding to the Curie temperatures of the two or more types (n types) of ferroelectrics is given, hence the authentication circuit has a superior forgery preventing ability. Since the property of the ferroelectric itself is utilized in the authentication circuit, even after a semiconductor device, an IC card or the like which includes the authentication circuit is manufactured, information can be written/erased to/from the storage area.
A second authentication circuit of the present invention comprises two or more ferroelectrics. Since the ferroelectrics have properties of retaining charges by residual polarization, the ferroelectric functions as a nonvolatile memory. In the ferroelectrics, authentication signals as secret information for making a semiconductor device or the like perform a predetermined function are stored. When only ferroelectrics 1 in the authentication circuit or the ferroelectric 2 is heated or cooled by means for thermally stimulating the ferroelectrics (such as heat generating device, cooling device, or the like) and held at a predetermined temperature and the ferroelectric 1 or the ferroelectric 2 is held at the Curie temperature of the ferroelectric 1 or the ferroelectric 2 or higher and the authentication circuit is held at a temperature lower than the Curie temperature of the ferroelectric different from the above, an authentication signal stored in the ferroelectric 1 or ferroelectric 2 is erased. Consequently, the authentication circuit is held at a predetermined temperature or less and operated, the authentication signal is output from the ferroelectric 1 or the ferroelectric 2 to the different ferroelectric, after that, the information stored in the ferroelectric 1 or ferroelectric 2 is erased. Subsequently, the authentication signal is output from the different ferroelectric to the semiconductor device or the like to make the semiconductor device or the like to perform a predetermined function. After that, the information stored in the ferroelectric 1 or ferroelectric 2 is erased. After performing these operations, a third person cannot nondestructively re-transmit an output signal of the semiconductor device or the like stored in the authentication circuit.
A semiconductor device of the present invention comprises at least an authentication circuit of the present invention. The authentication circuit for making the semiconductor device perform a predetermined function is held in a ferroelectric provided in the authentication circuit. The authentication circuit is provided with a plurality of ferroelectrics, and the authentication signals exist in the number equal to the number of the ferroelectrics provided in the circuit. Only when a predetermined temperature pattern corresponding to Curie temperatures of two or more types (n types) of the ferroelectrics is given, normal authentication signals are sequentially output. Thus, the semiconductor device has an excellent forgery preventing function.
An IC card of the present invention comprises at least an authentication circuit. An authentication signal for making the IC card perform a predetermined function is stored in a ferroelectric in the authentication circuit. The authentication circuit is provided with a plurality of ferroelectrics, and the authentication signals exist in the number equal to the number of the ferroelectrics. Only when a predetermined temperature pattern corresponding to Curie temperatures of two or more types (n types) of the ferroelectrics is given, normal authentication signals are sequentially output. Thus, the IC card has an excellent forgery preventing function.
In a first process for operating a semiconductor device of the present invention, a step for outputting at least one authentication signal from at least two types of ferroelectrics which comprise a ferroelectric 1 and a ferroelectric 2 having different Curie temperatures and properties of retaining charges by residual polarization to perform a predetermined function of the semiconductor device and erasing the at least one authentication signal stored in the ferroelectric 1 in the authentication circuit by giving temperature history of a predetermined temperature pattern is provided.
In a second process for operating a semiconductor device of the present invention, temperature history of a predetermined temperature pattern is given to some of the ferroelectrics in the semiconductor device having a second authentication circuit of the present invention. Authentication signals stored in ferroelectrics in the authentication circuit provided in the semiconductor device are sequentially erased, and a predetermined function of the semiconductor device can be performed.
In a first process for operating an IC card of the present invention, temperature history of a predetermined temperature pattern is given to the IC card of the present invention. The first process also includes a step for outputting at least one authentication signal from at least two types of ferroelectrics which comprise a ferroelectric 1 and a ferroelectric 2 having different Curie temperatures and properties of retaining charges by residual polarization to perform a predetermined function of a semiconductor device and erasing the at least one authentication signal stored in the ferroelectric 1 in the authentication circuit by giving temperature history of a predetermined temperature pattern, wherein the IC card comprises an authentication circuit which comprises at least two types of ferroelectrics comprising a ferroelectric 1 and a ferroelectric 2 having different Curie temperatures and properties of retaining charges by residual polarization, and when the authentication circuit is held at a Curie temperature of the ferroelectric 1 or higher and lower than the Curie temperature of the ferroelectric 2, an authentication signal stored in the ferroelectric 1 is erased.
In a second process for operating an IC card of the present invention, temperature history of a predetermined temperature pattern is given only to some of the ferroelectrics in the IC card having a second authentication circuit of the present invention. Authentication signals stored in ferroelectrics in the authentication circuit provided in the IC card are sequentially erased, and a predetermined function of the IC card can be performed. The IC card includes an authentication circuit which comprises at least two types of ferroelectrics which comprise a ferroelectric 1 and a ferroelectric 2 having properties of retaining charges by residual polarization, wherein the ferroelectric 1 is disposed near means for thermally stimulating the ferroelectrics, and the ferroelectric 1 is independently heated or cooled by the means for thermally stimulating, and an authentication signal stored in the ferroelectric 1 is erased by the means for thermally stimulating to perform predetermined function of the semiconductor device.